Cytoskeleton, Cilia, Flagella and Centrioles (Ultra Structure and Functions)

Introduction

Cytoskeleton, cilia, flagella and centrioles are vital components of a cell. Through their presence, they allow the prokaryotic and eukaryotic cells to function smoothly.Here, we learn about the structure and functions of these organelles.

Cytoskeleton

The cytoskeleton is a structure that keeps the cell’s shape and internal organisation while also providing support to the cell.

In the cytoplasm, a network of protein fibres exists that helps to maintain the cell’s shape, places cell organelles in correct positions, and allows cytoplasm, vesicles and other unicellular organelles to move within the cell. These protein fibres are collectively known as the cytoskeleton.

The cytoskeleton is made of the following types of fibres:

• Microfilaments
• Intermediate filaments
• Microtubules

Actin Filaments are the smallest cytoskeletal fibres, and they assist in the movement of cellular components during processes such as during cell division. Microvilli, the extensive folding of the plasma membrane found in cells dedicated to absorption, are also maintained by them.

Intermediate filaments are true skeleton of cells and serve structural functions like maintaining the cell’s shape and anchoring organelles. Keratin is a type of intermediate filament that helps to strengthen hair and nails.

The cytoskeletal fibres, microtubules, are the thickest. They are hollow tubes that can quickly dissolve and reform. These structures pull chromosomes to their poles during cell division and guide organelle movement. Flagella and cilia are also made up of these structural elements.

Function of Cytoskeleton 

The cytoskeleton is a structure that runs throughout the cytoplasm of a cell and controls a variety of functions.

• Assists the cell in maintaining its shape and provides support
• Keeps a variety of cellular organelles in place
• Aids in the development of vacuoles
• A dynamic structure that can disassemble and reassemble its components to allow for internal and overall cell mobility
• Movement of vesicles and other organelles inside and outside of a cell and chromosome processing during mitosis and meiosis are all examples of intracellular movement supported by the cytoskeleton
• Facilitation of cell migration for tissue repair and construction

Cilia and Flagella

Flagella (plural = flagellum) are long, hair-like structures that protrude from the plasma membrane and are used to propel a cell (for example, sperm, Euglena). A cell can only have one or a few flagella.

There are different types of flagella on the basis of the number of flagella present:

Monotrichous -single flagellum on the cell.

Peritrichous -flagella all around the cell.

Amphitrichous -flagella at both ends of the cell.

Lophotrichous -tuft of flagella at one end or both ends of the cell.

Atrichous – without flagella, nonmotile.

When cilia (singular = cilium) are present, they are numerous and extend across the plasma membrane’s entire surface. They’re short, hair-like structures that help move whole cells (like Paramecium) or substances along the cell’s outer surface (for example, there are cilia present in the fallopian tube which allows and helps the ovum to move towards the fallopian tubes).

Cilia may be of the following types:

Non-motile-They do not help in locomotion but are sensory in nature.Also termed as primary cilia.

Motile-They help in locomotion or movement of substance in a tube.

Functions of Cilia

• In isolated cells, cilia can be used to move around (e.g., Paramecium)

• To prevent disease, they use their rhythmic movements to sweep away substances, such as dirt, dust, microorganisms, and mucus from different places in the body

• Cilia are involved in the cell cycle and animal development, particularly in the heart

Functions of Flagella

• Flagella are used by cells such as the spermatozoon and protozoans such as Euglena to move around

• They play an important role in eukaryotic reproduction and cell feeding

• Flagella serve as propulsion mechanisms in prokaryotes, such as bacteria, and are the primary means by which bacteria swim through fluids

• They give pathogenic bacteria a way to help them colonise hosts and spread diseases

• Flagella also serve as scaffolds or bridges to help stick to host tissue

Centriole

A centriole is a cylinder-shaped organelle made up of a protein called tubulin.

Centrioles are submicroscopic microtubular subcylinders with a configuration of nine triplet fibrils and the ability to form duplicates, astral poles, and basal bodies without DNA or a membranous covering. 

They have a diameter of 0.15 um and a length of 0.3-0.5 um. They can be seen under a light microscope, but only an electron microscope can reveal the details of centriole structure.

Two centrioles are usually found together, but at right angles to one another. A pair of centrioles is known as diplosome. Diplosome is found in the centrosphere or kinoplasm (cytocentrum), a specialised part of the cytoplasm.

Function of Centrioles

• The formation of the spindle apparatus, which functions during cell division, is aided by centrioles

• Centrioles are missing in the mitotic process, causing divisional errors and delays

• Each cilium or flagellum has a single centriole that serves as the anchor point or basal body

• The formation of cilia and flagella is directed by these basal bodies

Conclusion

Cytoskeleton, cilia, flagella, and centrioles (ultra structure and function) is an important structure of the cell.They provide a framework to the cell.The flagella,cilia and centrioles are important.The cilia and flagella help in locomotion ,while cilia also help in movement of nutrient sor substances. Centrioles help in the process pf cell division thu helping a cell to continue to divide.